1. Field of the Invention
The present invention relates to in-cylinder injection, spark ignited internal combustion engine.
2. Description of the Background Art
When fuel is injected directly into a cylinder, an intake pipe does can have its wall surface unexposed to the fuel. This can ensure that an amount of fuel as required is supplied into the cylinder. For such an in-cylinder injection, spark ignited internal combustion engine, it has been proposed to spray fuel through a fuel injection valve into the cylinder in the form of a sector having a relatively small thickness and spreading vertically (see for example Japanese Patent Laying-Open No. 2000-220460).
If fuel is sprayed in such a vertically spreading sector in an intake process, the fuel readily disperses throughout the cylinder. Furthermore, fuel sprayed in such a sector has larger force of penetration than that sprayed in the form of a cone, and as it travels through the cylinder the fuel sprayed in the sector causes a large force of friction with intake air. The fuel thus tends to become fine particles and thus evaporate. A sufficiently homogenous air fuel mixture can thus be provided in the cylinder before ignition and satisfactorily homogenous combustion can thus be achieved.
An in-cylinder injection, spark ignited internal combustion engine can be required to provide not only homogenous combustion but also stratified combustion. For stratified combustion it has been proposed to spray fuel in the form of a vertically spreading sector in a compression process and utilize a vertical swirl to provide a combustible air fuel mixture directly in the vicinity of an ignition plug (see Japanese Patent Laying-Open No. 2000-22460 for example).
In stratified combustion, however, between fuel injection and ignition there is only a short period of time. As such, the fuel injected to provide the combustible air fuel mixture directly in the vicinity of the ignition plug, insufficiently evaporates. Furthermore, it is difficult to utilize the vertical swirl to ensure that the combustible air fuel mixture is positioned in the vicinity of the ignition plug.
This disadvantage associated with stratified combustion can be addressed by guiding the injected fuel to the vicinity of the ignition plug by utilizing a cavity formed at a top surface of a piston. This allows the injected fuel to receive heat from the cavity and thus sufficiently evaporate, and thus ensures that the combustible air fuel mixture is positioned in the vicinity of the ignition plug.
Typical cavity formed in a piston's top surface for stratified combustion can, however, hardly receive all of the fuel sprayed in the vertically spreading sector, and a relatively large amount of the fuel is sprayed outside the cavity and discharged as unburnt fuel resulting in poor exhaust emission.